I made up my mind long ago to follow one cardinal rule in all my writing — to be clear.

Experimentation is the least arrogant method of gaining knowledge. The experimenter humbly asks a question of nature.

Emotionally I am an atheist. I don't have the evidence to prove that God doesn't exist, but I so strongly suspect he doesn't that I don't want to waste my time.

I received the fundamentals of my education in school, but that was not enough. My real education, the superstructure, the details, the true architecture, I got out of the public library.

The day you stop learning is the day you begin decaying.

It is always useful, you see, to subject the past life of reform politicians to rather inquisitive research.

At two-tenths the speed of light, dust and atoms might not do significant damage even in a voyage of 40 years, but the faster you go, the worse it is--space begins to become abrasive. When you begin to approach the speed of light, hydrogen atoms become cosmic-ray particles, and they will fry the crew. ...So 60,000 kilometers per second may be the practical speed limit for space travel.